Method of and apparatus for withdrawing samples from molten metal baths



June 14, 1966 G. CAVALIER 3,255,634

METHOD OF AND APPARATUS FOR WITHDRAWING SAMPLES FROM MOLTEN METAL BATES June 14, 1966 G. CAVALIER 3,255,634

METHOD 0F AND APPARATUS FOR WITHDRAWING SAMPLES FROM MOLTEN METAL BATHS a Filed Nov. 13, 1962 4 Sheets-Sheet t Fl g. Z

l /l/l/ l l June 14, 1966 G. CAVALIER 3,255,634

METHOD OF AND APPARATUS FOR WITHDRAWING SAMPLES FROM l MOLTEN METAL BATHS Filed Nov. 13, 1962 4 Sheets-Sheet 3 /NVENI'DE G/BERT CH VH1/fe /213 Hrrawsy June 14, 1966 G. CAVALIER 3,255,634

METHOD oF AMD APPARATUS Foa wwnnnAwINe SAMPLES FROM MoLmmM METAL BA'rHs Filed Nov. 13, 1962 4 Sheets-Sheet L Ttrna In Fractions or o second Volume maken!! Vaiwm @E W@ Tim@ in #maana aF a seean 11Go 1 ooo remperol'ure of' mera! United States Patent O ice 3,255,634 METHOD OF AND APPARATUS FOR WITHDRAW- ING SAMPLES FROM MOLTEN METAL BATHS Gilbert Cavalier, Saint Germain-en-Laye, France, assignor to Institut de Recherches de la Siderurgie Francaise, Saint Germain-en-Laye, France Filed Nov. 13, 1962, Ser. No. 236,804 Claims priority, application France, Nov. 14, 1961, 878,790, Patent 1,313,201 Claims. (Cl. 73-425.6)

The present invention relates to a method of and to an apparatus for withdrawing samples from molten metal, such as iron or steel. More particularly, the invention relates to a method of and to an apparatus for obtaining samples of solidified metal which, without any further treatment, may be subjected to spectrographic analysis or to other types of tests.

It is customary to subject metallic substances to a spectrographic analysis which is a preferred way of testing metal because it can be carried out within very short periods of time. Attempts were made to provide a method according to which samples may be obtained in all stages of production and processing of molten iron, steel and other metallic substances. Samples withdrawn from molten metal are examinedwith a view to determine whether or not the molten substance is ready for pouring into molds.

Heretofore, samples of molten metal were withdrawn with the help of evacuated sampling tubes, i.e., with tubes from which air was evacuated prior to introduction of such tubes into a bath of molten metal. Suction prevailing in the interior of an evacuated sampling' tube will l cause the molten substance to penetrate into the tube, and

the height of the column will depend on the degree of evacuation, on the specific weight of the molten substance, on the diameter of the tube, and/ or on the melting temperature of the metal. However, it is a well known fact that molten material penetrating into the interior of an evacuated tube will splash and will form a series of layers along the internal surface of the tube, i.e., the sample is not of satisfactory consistency. Instead of obtaining a sample which resembles a solid rod, the resulting sample is a hollow body having a pronounced cavity along the entire or along the major part thereof and is often formed with a plurality of pores such as are found in a body of spongy consistency. Obviously, such samples are not suited for immediate spectographic analysis.

Accordingly, it is an important object of the present invention to provide a method of withdraw-ing samples from baths of molten metal according to which the samples are of such configuration and consistency that they may be tested in a spectrograph without any further processing.

Another object of the invention is to provide a method of the just outlined characteristics accord-ing to which one can obtain a sample which is without pores or blowholes and without so-called pipe such as is formed at the top of an improperly teemed ingot.

A further object of the instant invention is to provide Va method of the above described type accord-ing to which one can obtain samples which solidify during or immediately subsequent to withdrawal of molten metal from a bath so that the sample is ready for examination within exceptionally short periods of time.

An additional object of my invention is to provide a method of the above outlined characteristics which is equally suited for withdrawal of samples from molten ferrous or nonferrous substances.

Another object of the invention is .to provide an apparatus which may be utilized for carrying out a method of the above outlined characteristics.

3,255,634 Patented June 14, 1966 A further object of the invention is to provide an apparatus for withdrawing samples from molten metal which is constructed and assembled in such a way that it may be readily converted for withdrawal of samples from different types of molten metals.

.An additional object of the invention is to provide an apparatus which is capable of withdrawing highly satisfactory samples such -as may be subjected to spectrographic analysis or to other tests without any further processing and which withdraws samples in a fully automatic way. j

Still another object of my invention is to provide an apparatus of the above outlined characteristics which is of lightweight construction, which may be readily handled by semislrilled persons, which can be manipulated by a single person, and which can be reused as often as i desired.

Another object of the invention is to provide an apparatus which is capable of withdrawing molten metal without `any splashing and which will furnish satisfactory samples without any danger tothe operator.

An additional 4object of the invention is to provide an apparatus of the above outlined characteristics which may be readily adjusted to furnish samples of different lengths and which may be conveniently transported to different sources of molten metal so thatra single apparatus will suiice for obtaining samples from a large number of sources in a metallurgical plant.

With the above objects in View, the invention resides in the provision of a method of withdrawing samples from molten metal into heat-resistant sampling tubes I which comprises the steps of inserting one end of a sampling tube into a bath of molten metal (e.g., into 4aladle), and of gradually evacuating -air from the interior of the tube in such a way that the depression is a function of time whereby splashing and resultant formation of pipe or blowholes is prevented in a fully automatic way. In accordance with a feature of my method, t-he'interior of the sampling tube is maintained at atmospheric pressure up to the very moment when one end of the tube is inserted into molten metal, and I prefer to utilize a tube which is maintained at room temperature or at least at a temperature well below the melting point of the metallic substance so that metal which is sucked into the interior of such tube as soon as the evacuating step begins may solidify within a very short period of time.

lIt is often preferred lto regulate the evacuation of air in such a way that the drop of pressure is a linear function of time, i.e. that the evacuation progresses at the same rate as the duration of operation.

It will be seen that I provide a method according to which air may be evacuated from a sampling tube in such a way that pressure prevailing in the tube is reduced gradually while molten metal penetrates into the tube and, as explained hereinabove, the arrangement is preferably such that at the time it is immersed into molten metal the interior of the tube is maintained at a pressure which at least approximates atmospheric pressure. The rate at which pressure prevailing in the tube -is reduced is selected with a view to compensate for growing weight of metal which penetrates into the tube and also to compensate for increasing viscosity of the metal since the sample solidies within a very short period of time,

The method of my invention constitutes a substantial improvement over all such prior methods of which I am aware at this time. Thus, in addition to the .previously described method of using a sampling tube which is evacuated prior to insertion into molten metal, it was already proposed to preheat the sampling tube and to thereupon evacuate the tube prior to immersing one of its ends into a bath of molten metal. It was found that,

s) instead of being helpful, such preheating is rather detrimental because, as molten metal penetrates into an evacuated tube, it automatically raises the pressure prevailing in the tube since the volume of the air-containing space inthe tube decreases so that, if the metal is not permitted to solidify immediately or shortly after it penetrates into the tube, it will begin to drip from the tube. As a result of such dripping, the metal remaining in the tube will -form a substantially tubular sample because the material adhering to the wall of the tube will solidify more rapidly than the core.

It was also suggested to evacuate air with the help of a `spring biased piston which is released after one end of the sampling tube is immersed into molten metal. Such method has met with little success because a suddenly moving piston produces an instantaneous drop in pressure so that molten metal drawn into the tube behaves in the same way as if the tube were evacuated prior to its immersion into the bath. Experiments conducted with spring-biased evacuating pistons have shown that molten metal will splash onto the walls of the sampling tube and will form a sample which exhibits pronounced pipe and blowholes.

Furthermore, a piston which is biased by a spring will perform a suction stroke at such a high rate of speed that the evacuating step is completed before the metal has a chance to attain a desired height in the interior of the sampling tube. Therefore, at least during a portion of the sampling operation, molten metal must rise into a preevacuated portion of the sampling tube which is tantamount to evacuation prior to immersion into the bath. In other words, .pressure is not being reduced during the entire duration of penetration of molten metal into the sampling tube. In fact, as soon as the spring-biased plunger reaches the end of its suction stroke, pressure prevailing in the empty space of the sampling tube begins to rise since the volume of such empty space decreases at the same rate at which molten metal continues to enter into the tube. On the other hand, themethod of my invention is carried tout in such a way that pressure is reduced continuously despite the fact that thevolume of the empty space in the tube decreases while molten metal is being drawn from the bath. Therefore, and particularly since I also take into consideration the fact that the viscosity lof metal already contained in the tube increases at a rapid rate, the sample obtained in accordance with my method is of exceptionally satisfactory homogeneousness and is without cavities so that it is ready for testing in a specltograph or in another apparatus.

The apparatus of my invention comprises a sampling f tube of heat resistant material (such as silica) one end of which may be inserted into molten metal, and adjustable pressure reducing means connected to the other end of the tube. Such pressure reducing means may comprise a cylinder and plunger assembly whose cylinder is communicatively connected with the sampling tube, and means for reciprocating the plunger at a predetermined speed so that the rate at which the plunger may evacuate air from the sampling tube may be adjusted and varied within a desired range.

The means for reciprocating the plunger may comprise a pneumatically opera-ted motor or an electric mot-or, and I prefer to construct the reciprocating means in such a manner tha-t the plunger is arrested n a fully automatic way when it completes a suction and a return stroke or immediately after it completes a suction stroke.

` Certain other features of my apparatus reside in the provision of specially constructed adjusting means for the aforementioned reciprocating means, in the provision of a readily separable connection between the sampling tube and the remainder of the apparatus, in the provision of means which shields the operator from the molten metal at the time a sample is being withdrawn from the bath, and in the provision lof a specially constructed sampling tube which forms samples of such smoothness that they may be used in various testing devices without any further processing.

The apparatus of my invention is preferably constructed in such a way that, when the apparatus is put to use, the pressure prevailing in the sampling tube decreases despite the fact that molten metal penetrates into the tube. As a rule (but not necessary), the apparatus comprises a cylinder whose chamber is connected to the tube and a plunger which is reciprocated by a motor so that it may evacuate air from the tube while moving in a given direction. The motor may but need not move the plunger at constant speed. The time interval during which the plunger performs an evacuating stroke at least equals the time interval during which molten metal penetrates into the sampling tube, i.e., the evacuation `of air is continued at least until such time when molten metal ceases to rise in the sampling tube.

The novel features which are considered as characteristic -of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following detailed description of certain specific embodiments with reference to the accompanying drawings, in which:

FIG. 1 is an axial section through an apparatus which embodies one form of my invention and which is operated by compressed air;

FIG. 2 is an axial section through a modied apparatus which is operated by electric current;

FG. 3 is an enlarged axial section through a portion of the modified apparatus, showing a reversing device which serves as a means for automatically reversing an electric motor;

FIG. 4 is a diagram showing the electric circuit of the modied apparatus;

FIG. 5 is an axial section, at a larger scale, of a portion of the apparatus according to FIG. l;

FIG. 6 is a diagram wherein the curves represent the drop of pressure of a sample tube during withdrawal of molten metal by means of conventional apparatus and by an apparatus which embodies the present invention;

FIG. 7 is a similar diagram wherein the curves represent the ratio volume metal volume of tube in sampling tubes which form part of known apparatus and of apparatus which embodies the present invention; and

FIG. 8 is a further diagram wherein the curves represent mean temperatures of metallic samples during withdrawal from a bath by means of conventional apparatus and by an apparatus which embodies my invention.

Referring now in greater detail to the illustrated embodiments, and first to FIG. 1, there is shown ,an apparatus which is utilized for withdrawing samples from baths of molten metal, such as molten steel or molten iron. The apparatus comprises a heat-resistant tubular member 15, hereinafter called sampling tube, whose lower end may be inserted into a bath M of molten iron contained in a ladle L. The means for reducing the pressure prevailing in the interior of the tube 15 comprises a pneumatic motor including a double-acting cylinder-and-piston assembly which comprises an outer cylinder 1 having a downwardly extending nozzle 23 whose lower end is detachably coupled to the upper end of the tube 15 by a connecting means here shown as a resilient sleeve 16 consisting of rubber or the like. The material of the tube 15 should be capable of resisting temperatures which prevail in a bath of molten metal; for example, this tube may consist of refractory material.

The internal chamber 1a of the outer cylinder 1 accommodates an annular piston 2 having an upwardly extending hollow tubular piston rod 2a into which is telescoped an inner cylinder 3. This cylinder 3 is rigid with the outer cylinder 1 and is coaxial with the nozzle 23. The chamber 3a of the inner cylinder 3 accommodates an elongated air evacuating plunger 4 whose upper end is secured to an internally threaded cap 5 (see the screw 5a). This cap constitutes a coupling between the plunger 4 and the piston rod 2a and is provided with internal threads mating with external threads at the upper end of the piston rod which latter extends through an annular collar 1b forming part of a threaded cover 1c which is screwed into the upper end of outer cylinder 1. It will be noted that the cap 5, the screw 5a and the piston rod 2a form a motion transmitting means providing a rigid connection between the piston 2 and the plunger 4, and this connection. compels the plunger to reciprocate in the inner chamber 3a when the piston reciprocates in the outer chamber 1a. The piston 2 is provided with a circumferential groove for an O-ring 17 which is in sealing engagementwith the internal surface of the outer cylinder 1 to prevent leakage of pressure fluid between the upper andlower portions of the chamber 1a. A similar sealing ring 1S is accommodated in a circumferential groove provided at the lower end of the plunger 4.

v The lower portion of the cylinder chamber 1a communicates with a pipe 11 leading to a channel 10 provided in a reversing valve 7 which is detachably secured to a nipple 1e fixed to the upper portion of the outer cylinder 1. The connection between the nipple 1e and the valve 7 comprises an internally threaded annular nut 1f. A second channel 8 of the reversing valve 7 communicates with a duct 1g leading to the upper portion of the cylinder chamber la. Suitable gaskets 13 and 14 prevent leakage of compressed uid between the nipple 1e and the valve 7 as well as between the channels 8, 10. The means for alternately admitting compressed uid to the channels 8, comprises a manually operable valve member 9 whose stem 9a extends through a transverse bore 7a drilled into the body of the reversing valve 7. The length of the stem 9a exceeds the length of the bore 7a and its lower end, as viewed in FIG. 1, is connected to a screw 21 whose head acts as a stop by normally abutting against the underside of the reversing valve 7 in response to the bias of a helical spring 21a which is inserted into the bore 7a and which acts between an internal shoulder 7b of the reversing valve and a collar 9b on the stem 9a- The diameter of the head of the screw 21 is greater than the diameter of the passage in the shoulder 7b so that the spring 21a cannot eject the valve member 9. In the position of FIG. 1, the collar 9b prevents the ow of compressed fluid from a supply pipe 6 to the channel 10, and a second collar 9c of the stem 9a simultaneously seals the upper end of the bore 7a while permitting compressed fluid to flow from the pipe 6 through the channel 8 and duct 1g and into the upper portion of the cylinder chamber 1a. In other words, the fluid is free to move the piston 2 to its lower end position in which this piston expels fluid from the lower portion of the cylinder chamber 1a. The pipes 6, 11, the channels 8, 10 and the duct 1g together constitute a conduit means which connects a source 6a of compressed fluid with the chamber 1a at the opposite sides of the piston 2.

When the operator depresses the head of the valve member 9 against the bias of the spring 21a, the collar 9c seals the pipe 6 from the channel 8 but the collar 9b permits compressed fluid to flow through the channel 10 and pipe 11 into the lower portion of the cylinder chamber 1a. At the same time, the collar 9c permits escape of spent fluid through the channel 8 and through the upper end of the bore 7a so that the piston 2 may move upwardly to entrain the plunger 4 which evacuates air from the interior of the sampling tube to thereby draw molten iron from the ladle L at a speed which is determined by an adjusting screw 12 serving as a means for regulating the rate of fluid ow through the channel 10. This adjusting screw is preferably provided with a pointed tip and its threads mate with internal threads of a bore 7c in the valve 7, this bore communicating with the channel 10. It will be readily understood that, by turning the screw 12, an operator may regulate the rate at which compressed fluid can flow to the underside of the piston 2 to thereby control the speed at which the plunger 4 moves to its upper end position. In other words, the screw 12 may adjust the speed at which pressure in the tube 15 drops and hence the rate at which molten iron rises in this tube.

The head of the valve member 9 is provided with one or more projections 9d which prevent it from sealing the upper end of the bore 7a when the valve member is depressed against the bias of the spring 21a. One or more fluid evacuating ports 7d which communicate with the bore 7a at a point close to the shoulder 7b permit the fluid to escape from'the channel 10 when the valve member 9 is depressed.

A fluid-permeable filter 19 is inserted into the outer cylinder 1 to prevent entry of metal into the inner chamber 3a. This filter may -compn'se several layers (for example, three layers) of line netting consisting of nickel Wire with a diameter of 0.5mm. As shown, the filter 19 is accommodated in a recess provided in the underside of the outer cylinder 1 and is retained therein by a threaded boss 23a which is rigid with the upper end of the nipple 23 and which is screwed into the outer cylinder. A gasket 20 prevents leakage of air about the boss 23a.

A tinted panel 22 of translucent material (e.g., plexiglass) is secured to the lower end of the cylinder 1 lby a cap screw 22a and enables an operator to observe without any danger t-o his eyes the tube 15 at the time the latter is immersed into the bath M. For example, the panel 22 may be tinted green.

In the embodiment of FIG. l, compressed lluid supplied by the pipe `l5 is air delivered by a suitable source here shown as a compressor `6a'.

The apparatus of FIG. l operates as follows:

Atthe time an operator desires to withdraw a sample from the bath M, the piston 2 assumes the position of FIG. 1 because the lower portion of the outer cylinder chamber 1a is free to communicate with the atmosphere via port 7d and because the pipe 6 communicates with the duct 1g, i.e., the collar 9b of the valve stem 9a seals the supply pipe 6 from the channel 10 because the valve member 9 is in itsinoperative position. The pressure prevailing in the sampling tube 15 equals `atmospheric:

pressure.

The operator then inserts the lower end of the sampling tube 15 into the bath M and depresses the valve member 9 to its operative position so as to connect the pipe 6 with the lower portion of the chamber 1a whereby the plunger 4 is caused to ascend and to reduce the pressure prevailing in the interior of the sampling tube. Molten iron begins to rise and forms in the tube 15 a s-olid column or bar Whose height depends on the ratio of the Volume of the inner chamber 3a to the volume of the tube 15. When the plunger 4 reaches the upper end of its stroke, the operator releases the valve member 9 and withdraws the tube 15 from the bath M. The tube 15 is then de? tached from the nipple 23 and the sample is removed to be subjected to spectrographic examination in a manner not forming part of this invention. Once the head of the valve member 9 is released, the spring 21a immediately returns the stem 9a to the idle position of FIG. l and the piston 2 automatically descends to its lower end position because the pipe 6 is free to communicate with the duct 1g while air contained in the lower portion of the outer cylinder chamber 1a is free to escape via port 7d. The speed at which the plunger 4 is caused to rise in response to depression of the valve member 9 depends on the position of the adjusting screw 12, i.e., on the extent to which the tip of this screw obstructs flow of compressed uid into the conduit 11.

The ratio between the effective surfaces of the piston 2 and plunger'4 is sufficiently large to insure that the speed at which the plunger 4 rises depends mainly on the position of the adjusting screw 12. Also, the internal diameter of the tube 15 is suiciently small to insure that the speed at which the plunger 4 rises is not affected by the fact that the lower end of the tube 15 is sealed at the time this tube dips into the bath M. For example, the air evacuating action of the plunger 4 may be selected in such a way that a sampling tube having an internal diameter of 3.5 mm. would draw 8 cm.3 of water while the plunger 4 moves from its lower to its upper end position. This would correspond to withdrawal of 3 cm.3 of mercury from a mercury bath, i.e., to a column having a height of close to 30 cm. Under ideal conditions, the same apparatus would withdraw a sample bar of molten iron with a height of about 40 cm. However, the height of the sample bar is always less than 40 cm. because the metal is cooled very rapidly and hardens in the tube.

The speed at which the plunger 4 rises may be in the range of 10 cm./sec., but such speed will be changed slightly if one wishes to use the apparatus rst for withdrawal of molten iron and thereupon for withdrawal of molten steel or vice versa.

It will be noted that, in contrast to conventional apparatus of which I am aware at this time, the apparatus of FIG. l begins to evacuate air only after the tube is inserted into the bath M and that such withdrawal of air is gradual. In other words, at the time the lower end of the tube 15 is immersed into molten metal, the interior of this tube is maintained at atmospheric pressure, and the pressure thereupon drops gradually to avoid splashing of metal. Such splashing will occur invariably whenever an evacuated tube is immersed into a metal bath. Splashing is due to the fact that a stream of molten metal is sucked at great speed when one end of an evacuated tube is immersed into the bath. The aspirating effect of an evacuated tube A causes the metal entering the evacuated space to ascend along the walls of the tube and to form a series of layers or laminations which in their entirety constitute a tubular rather than a solid baror rod-like sample. At the very best, the sample obtainable with an evacuated sampling tube is of spongy consistency having at its upper end a depression analogous to so-call'ed pipe which develops in the upper portions of ingots. Such tubular or spongy (i.e., highly porous) samples are not suited for spectrographic analysis or for other types of tests.

FIGS. 2, 3 and 5 illustrate a modified apparatus wherein the evacuating plunger 4 is operatively connected with an adjustable reciprocating means here shown as including a single-phase electric motor 24. The lower part of FIG. 2 shows a cylinder 1 which is analogous to the cylinder 1 of FIG. l and wherein analogous parts are identied by reference numerals used in FIG. l each followed yby a prime. V

The motor 24 comprises a wound stator 25 and a rotor 26 mounted on and driving an internally threaded tubular shaft 27 which is journalled .in bearings 28, 29. A collector 30 which rotates with the shaft 27 is contacted by spring-biased brushes 31, 32 in a manner well known in the art of such motors.

The shaft 27 serves as a means for reciprocating a cylindrical sleeve 33 which is provided with external threads mating with internal threads of the shaft 27. The lower end of the sleeve 33, as viewed in FIG. 2, lits rigidly connected with the upper end of the plunger 4. It will be noted that the parts 27, 33 constitute a means ttor transforming rotary movements of the rotor 26 into linear movements of the plunger 4'. This plunger is formed with an axial-ly extending blind bore 34 whose upper end is open to receive with play the lower end portion of a push rod 35. When the shaft 27 rotates in a sense to move the sleeve 33 upwardly, as viewed in FIG. 2, and when the sleeve 33 approaches the upper end of its stroke, the lower end of the push rod 35 comes into abutment with the bottom wall 36 of the blind bore 34 and Ithe push rod 35 is lifted suliciently to actuate a reversing means 37 in orderto change the direction of the rotor 26. The housing 73 `of the vreversing Imeans 37 (shown in greater detail in FIG. 3) is mounted on the casing 24a of the motor 24. As `soon as the direction of rotation of the rotor 26 and of the shaft 27 is reversed, the sleeve 33 begins to descend and ymoves the plunger 4' toward the lower end of the cylinder 1', i.e., toward the nozzle 23.

The push rod 35 is provided, as shown more clearly in FIG. 5, with a collar 38 which is spaced from its lower end. The diameter of the collar 38 is smaller than the diameter of the blind bore 34 but greater than the diameter of the passage in an inwardly extending annular `flange provided at the upper end of a cup-shaped entraining member 39 which is screwed into the upper end of the sleeve 33. The purpose of the member 39 is to engage the collar 38 and to move the` push rod downwardly when the sleeve 33 approaches the lower end of its stroke. The arrangement is such that, when the member 39 engages the collar 3S entra-ins the push rod 35 through a predetermined distance, the push rod causes the reversing means 37 to shut off the supply of electric current to the motor 24, i.e., to arrest the plunger 4' in its lower end position. It will be noted that the push rod 35 constitutes -a trip which is adapted to actuate the reversing means 37 in a sense to reverse the direction of the rotor 26 when the plunger 4 moves to its upper end position and to arrest the motor 24 Iwhen the plunger moves to its lower end position.

The apparatus of FIGS. 2, 3 and 5 further comprises means for pre-venting rotation of the assembly including the plunger 4', the sleeve 33 and the entraining member 39. This means comprises an inwardly extending tooth 41 which is lixed to the cylinder 3' and which extends into an elongated axially parallel slot 40 of the plunger 4.

The construction of the reversing mean-s 37 is shown in `FIG. 3. The purpose .of this reversing means is to start `the motor 24 in response to actuation of a pushbutton forming part of a starter switch 75 (see FIG. 4), so that the motor will cause the plunger 4 to perform an upward lstroke in order to evacuate air from the nipple 23' and r.from the sampling tube (not shown in FIGS. 2-5), to thereupon reverse .the direction of the rotor 26 whereby the plunger 4 performs a downward stroke, and to automatically arrest the motor when the plunger 4 approaches `the end of its downward stroke.

The reversing means 37 comprises the aforementioned lhousing 73 which accommodates an insulating shell 42 ifor a series of axially spaced dixed `annular contactors' 43, `44, 45, 46, 47 and 4S. These contactors may consist of copper and are respectively spaced by insulating rings 49, 50, 51, y52 and 53. The upper end of the shell 42 is closed by a cover 54 of insulating material which is secured to the top wall of the housing 73 by screws 74. The cover `54 is screwed into the upper end of Ithe she-ll 42 and causes the stack of contactors 43-'48 and rings 49-53 to abut against the upper end face of an insulating bottom wall 55 which is received in Ithe lower end of the shell. In other words, the lowermos/t contactor 43 bears against the bottom wall 55 and the uppermost contactor 48 bears against the underside of the cover 54.

rIlhe contaotors 43-48 are respectively in current conducting contact with terminals 56, 57, 58, 59, and 6'1 which are screwed into and which extend radially outwardly through. the shell 42. Selected pairs of these fixed contactors 43-48 may come into contact with-a pair of axially movable sliding contactors 62, 63 which are accommodated in the space defined by the stack 43-48, 49453. Each sliding contactor comprises two semicircular or U-shaped sections which are biased apart by a spring 65. These springs are accommodated in diametral slots provided in an insulating head 64 which is secured to the upper end of the push rod 35 by a diametral pin 66. Thus, the springs 65 compel the respective sliding contactors to rem-ain in current conducting contact with selected pairs of xed contactors, depending on the axial position of the push rod 35. As explained hereinabove, the rod 35 is caused to perform an axial movement only at the time Ithe plunger 4 approaches the upper or the lower end of its stroke. FIG. 3 illustrates the push rod 35 in a position it assumes when thep-lunger 4' has been moved to the upper end position, i.e., atter the .plunge-r has caused a predetermined quantity of molten metal to penetrate into the sampling tube. The contactor 62 contacts the contactors 47, 418 and the contactor 613 engages the contactors 45, 46. fIn Isuch position of the rod 35, the rotor 2 6 is driven in a direction -to move the plunger 4 downwardly, i.e., toward the nozzle 23.

When the plunger 4 approaches the lower end of its stroke, the member 39 entrains the `collar 38 to move the push rod 315 in downward direction (iFIG. 2). As soon as the contactor 62 moves away from the cont-actor 48, the circuit of the motor 2'4 is open but the inertia of moving parts is such as to cause rotation of the shaft 27 for a period of ltime which is sulicient 'to move a shoulder 67 at the underside of rthe head 64 against a currentconducting washer 68 which normally engages the underside of the lowermost contactor 43 because it is under the bias of a spring '69. This spring is mounted between an upwardly facing internal shoulder 55a of the bottom wall 55 and the underside of the washer 68, the latter being rigidly connected with a conductor 70 which passes through an axially parallel slot '7'1 provi-ded in the shell 42. The distance which the shoulder 67 must cover after the circuit of the motor 24 has been opened m-ay be in the range of several millimeters which is sufficient to move t-he washer 68 away from the contactor 43. The washer 68 constitutes the moving Contact of a switch whose fixed contact is the contactor 56. This switch 56, 68 is installed in the circuit of -a source 77, 718 of electrical energy so that, when the washer 68 moves away from the contactor 56, the supply of electric current to the motor 24 is shut ott to prevent unintentional lifting of the plunger 4. The source of electrical energy (represented by the terminals 77, 78) is shown in FIG. 4. When the switch 56, 68 is open, the upper contactor 62 bridges the terminals 59, 60 and the lower contactor 63 bridges the terminals 57, 58, which means that the circuit of the motor 24 would rotate the rotor 26 in -a sense to move the plunger 4 upwardly, provided the. switch 56, 5'8 or the starter switch 75 is closed. When the operator desires to obtain a new samip-le, he merely depresses the pushbutton of the switch 75 whereby the source 77, 78 'supplies current to the motor 24 Vand the latter begins to move the plunge-r 4 in upward direction.' As the plunger 'moves upwardly, the entraining member 39 moves away from the collar 38 and the push rod 35 is free to follow the Ibias ofthe :spring 69 which then moves the washer 68 against the contactor 56 to insure that the motor 24 is connected with the source 77, 7'8 even if the operator releases the pushbutton of the switch 75. 'Phe operation is then continued in a fully automatic way because the push rod 35 moves upwardly as soon `as its lower end comes into engagement with the bottom wall 36 of the blind bore 34 to return the contactors 62, 63 to the position of FlG. in which the direction of the rotor 26 is reversed. The sampling tube may -be detached from the nozzle 23' before the plunger 4' begins its downward stroke. As explained hereinabove, the circuit oit' .the motor 24 is open for a short period of time before the plunger 4' reaches the lower end of its stroke because the contactor 62 moves away from the contactor 48 but the inertia of moving parts is suicient to entrain the shoulder 67 into engagement with the washer 68 which is depressed against the bias ofthe spring 69 to disconnect the source 77, 78 from the motor 24.

'Ihe opening in the bottom wall 55 is sealed by a co'pper ring 72 which serves as a bearing for the push rod 35.

FIG. 4 shows the sliding contactors 62, 63 in two dif- [ferent positions. IIn their full-line positions, these contactors respectively bridge the terminals 60-61 and 58- 59. In their dotted-line positions 62a, 63a, the contactors 62, 63 respectively bridge the Iterminals 59-60 and 5='7-58. The washer 68 moves to its broken-line position 68a when it is out of contact with the contactor 43 and terminal 56. A variable resistance 716 serves as a means for adju-sting the speed of the rot-or 26 and for thereby adjusting the speed at which the plunger 4 moves between its end positions. =In other words, the resistance 76 per- 'forms the same function as the adjusting screw 12 off FIG. 1.

sReferring .to FIG. 6, there is shown a diagram with curves a, b and c which arel respectively illustrative of pressures prevailing in sampling tubes forming part of two conventional apparatus (curves a and b) and in the sampling tube 15 of an apparatus of the type shown in FIG. l or in FIGS, 2-5 (curve c). 'lihe curve a illustrates -how the pressure in a sampling tube varies if the tube is evacuated prior to immersion into a bath of molten metal. It will be noted that the pressure rises very rapidly as #soon `as the tube is immersed into the 'bath because the |volume of its internal space decreases within a few fractions of a second. This is due to the :fact metal rises with a sudden splash.

The curve b is indicative of pressures prevailing inv ya sampling tube which .is evacuated by a spring-biased plunger. rapidly so that it invariably causes splashing of molten metal along the internal surface of the sampling tube.

The curve c indicates that evacuation of the sampling tube 1'5 is gradual so that no' splashing occurs and that the sample withdrawn from a bath may assume the form of a solid rod. Thus, while the curve b indicates that a sampling tube which is evacuated by means of a spring already constitute-s an improvement over a sampling tube (curve a) which is evacuated prior to immersion into the b-ath, FIG. 6 shows that gradual drop in pressure (as indicated by the curve c) will insure gradual withdrawal of molten metal without splashing and without resultant pipe or blowholes in the hardened bar.

The curves shown in the diagram of FIG. 7 illustrate the rate at which a sampling tube is filled with molten metal in an ideal apparatus (curve a), in an apparatus which evacuates the ltube prior to immersion into the bath (curve b'), in an apparatus whose sampling tube is heated prior to immersion into the bath (curve c), and in the apparatus of my invention (curve d). Curve b' shows that molten metal rises very rapidly and that the nate of ascent thereupon suddenly drops to zero which is indicated by the horizontal portion of this curve. illustrates that a preheated tube is lled within a small lfraction of a second and that molten metal thereupon -1i'lows back into the bath because it does not harden in the tube. This is due to the fact that a preheated tube prevents rapid hardening or the samiple. It will be noted -fthat It-he curve d approaches rather closely the .ideal curve a', i.e., the sampling tube 15 of my apparatus is `dilled gradually because it is not preheated and because Ithe plunger 4 or 4 insures that evacuation of air is gradual and is proportional to the speed at which molten metal rises in this tube.

The curves a" and b in the diagram of FIG. 8 illustrate the rate at which a sample is cooled in the sampling tube 15 (curve a) and in a preheated tube (curve b). It will be noted that metal in a preheated tube does not harden at the same rate at which it is being withdrawn from the ybath (compare curves b" and c'), whereas `a tube which is maintained at room temperature or at a temperature well below the melting point of the metal insures that the metal hardens at the same rate at which it is being sucked from the bath (compare curves a and d'). The total time necessary for withdrawing a samp-le from the bath is normally less than one-fifth of a second, this being the time necessary to allow for hardening of a that molten This curve shows that :the pressure rises very Curve c "t il vsample bar whose length is between about -30 cm. The apparatus of my invention is especially suited for withdrawal of samples from .ladles. The ladle is filled with molten metal which is withdrawn from an openhearth furnace, from a converter or from another source of molten metal, and the lower end of the sampling tube is then dipped into the liquid material. In the next step, the operator depresses the head of the valve member 9 (FIG. l) or the pushbutton of the switch '75 (FIGS. 2-5). If the apparatus is used for withdrawal of samples from a bath of molten steel, it is applied after the usual deoxidation. As a rule, the entire operation including the filling of a ladle may be completed within 30 seconds. The surfaces of bars obtained upon soliditication of molten metal are glossy and free of oxide layers. If the surfaces of the sampling tube are finished to a high degree of polish, the surfaces of the samples are equally smooth, and I have found that the samples are perfectly quenched. The cooling occurs rapidly since, and as explained hereinabove, a bar with a length of l030 cm. and with a diameter of about 3.5 mm. will harden within a fraction of a second. In fact, withdrawal and hardening of a sample bar are completed even before the plunger 4 or 4 reaches the upper end of its stroke. To insure that the `bar cools without further delay, the tube is removed from the nozzle 23 or 23' and is dipped into a water bath.

The samples obtained with the apparatus of my invention are of exceptionally good homogeneousness not only in longitudinal but also in transverse direction. When samples are drawn from phosphor-containing or hematite iron, there is no appreciable precipitation of graphite which is of considerable importance for determination of carbon contents by sepectrographic analysis.

One of the most important factors which intiuence the quality of sample bars is the rate at which pressure is being reduced in the sampling tube during withdrawal of molten metal from a lbath (FIG. 6). The total time of withdrawal is of lesser importance provided, of course, that such total time is less than the time necessary for solidication of the sample. Thus, as long as the apparatus of my invention is capable of regulating the evacuation of air in a manner to insure that pressure in the interior of the tube drops gradually, i.e., that such pressure is not permitted to rise while molten metal is being withdrawal, splashing with resultant lamination, porousness and/ or tubularity of the sample will be avoided. As explained hereinabove, I prefer to construct the apparatus 1n such a way that, during withdrawal of a sample, the pressure prevailing in the interior of the sampling tube decreases gradually and that such drop in pressure occurs at a more or less constant rate.

Any rapid changes in evacuation of air from the interior of the molten tube will cause splashing With all such detrimental effects which have been pointed out hereinabove.

The temperatures prevailing in the bath of molten metal do not have too much bearing on the operation of the apparatus. However, such temperatures must be taken into consideration in determining the dimensions and in selecting the material of the sampling tube. As a rule, a sampling tube used for withdrawal of samples from molten iron may -be used for withdrawal of samples from molten steel. While a tube made of Pyrex (trademark) will be satisfactory for withdrawal of samples from molten tin, a tube with greater resistance to heat .(such as one consisting of pure silica) should 'be used 1n connection with molten iron or steel.

Another rather important factor which must bev consid-ered in selecting the dimensions and the material of a sampling tube is the difference between the temperature of molten metal and vthe temperature at which the sample chills. This difference does not vary beyond a certain range (about 200 C.) even if one deals with greatly different types of metals. As a rule, such difference is less if the melting point of a metal is rather low. I have found that, if the material of the sampling tube exhibits a great resistance to heat, the same tube may be used with many different types of metals. Of course, a sampling tube which is just resistant enough to stand a temperature corresponding to the melting point of tin cannot be used for withdrawal of samples from a bath of molten iron. On the other hand, a sampling tube which can withstand temperatures in the range of 1,600 C. and which can also withstand rapid cooling to a temperature at which molten tin begins to solidify will be made of a material which is different from the material selected for a tube which is used exclusively for withdrawal of molten iron or the like, i.e., a material which solidifies at much higher temperatures.

A further factor which inuences the selection of material for the sampling tube is the specific heat of the metal and the rate at which molten metal can transmit heat to the walls of the sampling tube. Such factors influence the rate of speed at which the sample chills because they determine the rate of heat exchange 'between the metal and the surrounding air. The influence of these factors is rather difficult to determine with great accuracy since the area of contact between the sampling tube and the material which is being withdrawn from a bath of molten metal varies continuously when the material is sucked into the tube, i.e., the area of contact increases in dependency on the diameter of the tube and on the extent of evacuation of air from the tube.

The internal diameter and the wall thickness of the sampling tube determine the diameter and the cubic contents -of the sample. Consequently, the dimensions of the sampling tube determine the rate at which the sample chills and hence the ycrystalline structure of the sample. Furthermore, the dimensions of the tube affect the dynamic conditions which exist during withdrawal of molten metal, particularly the inuence of surface tension which, in turn, inuences the length of the sample and the speed at which molten metal rises in the tube. The diameter of the tube may be selected arbitrarily within a certain range provided, of course, that the remaining factors which inuence the length, the structure and the cooling of a sample are selected in conformity with such arbitrarily selected value. I have found that it is of considerable advantage if the speed at which air is being evacuated from the interior of the sampling tube is-selected in conformity with the characteristics of a particular metal. For example, the wall thickness of the sampling tube will be selected in dependency on the characteristics of the material of the tube and on the difference between the melting point and the soliditication temperature of the metal. Also, it is generally desirable to select the volume of the space in the evacuating cylinder 3 or 3 in dependency on the nature and temperature of a particular metallic substance. For example, the ratio between the useful volume of the space in the cylinder 3 or 3' and the volume of the space in the sampling tube will be about 2:1 when the apparatus is used for withdrawal of samples from molten iron, whereas such ratio is preferably about 10:1 or even 20:1 when the apparatus is used for Withdrawal of samples from molten steel.

An additional important factor which influences the quality of samples is the nish of internal surface of the sampling tube. As a matter of fact, insofar as I am informed at this time, this factor may exert a major influence on the quality of samples. An important requirement is that there be no generation of gases at the time the sampling tube is heated by contact with molten metal. Consequently, I prefer to avoid using sampling tubes which consist of frit (i.e., of a substance using sand as starting material). In such materials, large quantities of gases are entrapped in the pores between the individual particles and, when molten metal penetrates into the tube, such gases are heated and expand to thereby increase the pressure in the tube with resultant expulsion of molten metal back into the bath. Therefore, I normally prefer to use heat-resistant materials which are free of pores and without gas bubbles. For the same reasons, I prefer to avoid using sampling tubes whose internal surfaces are coated with films consisting of a substance which is likely to produce gases in response to decomposition at elevated tempertaures. A very satisfactory material for use in the manufacture of sampling tubes to be employed in the apparatus of my inventionV is fused quartz, Such material may be used for the production of transparent sampling tubes which enable an operator to observe the formation of a sample bar. However, sampling tubes made of lowquality pure silica will do in many instances since the presence of minor quantities of gases will have no appreciable detrimental effect on the withdrawal of molten metal.

The appartaus of my invention may be put to use at all stations of a metallurgical plant, such as at the point where metal is tapped from a furnace, on the platforms of steel manufacturing plants, in blast furnaces and elsewhere. As will be readily apparent upon perusal of the preceding description, the manipulation of my apparatus requires very little skill so that the apparatus may be entrusted to semiskilled or unskilled workers. Regardless of whether the reciprocating means for the evacuating plunger 4 or 4 is actuated by compressed fluid or by electric current, the apparatus may be put to use without necessitating the provision of special conduits or conductors since outlets for electric current as well as valves for connection to a source of compressed air are always available in all modern metallurgical plants.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features, that, from the standpoint of prior art, fairly constitute essential characteristics of the generic and specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured byy Letters Patent is:

1. A method of withdrawing a sample from molten metal into a sampling tube, comprising the steps of mainf taining the material of the tube at a temperature not substantially exceeding room temperature; inserting one end of the tube into the metal; and gradually reducing the pressure prevailing in the interior of the tube by evacuating air through the other end thereof in such a way that the drop of pressure grows in direct proportion with the time elapsed since the beginning of withdawal whereby the metal penetrates gradually into the tube.

2. A method of withdrawing a sample from a molten ferrous substance into a heat-resistant sampling tube, comprising the steps of inserting one end of the tube into the ferrous substance; and gradually reducing the pressure prevailing in the interior of the tube by evacuating air through the other end thereof in such a way that the pressure decreases in direct proportion with the time elapsed since the beginning of withdrawal whereby the ferrous substance penetrates gradually into the tube.

3. An apparatus for withdrawing samples from molten metal, comprising la sampling tube of heat-resistant material, said tube having a first end adapted to be inserted into molten metal and a second end; pressure reducing means connected with said second end for evacuating air from said tube yand for thereby causing molten metal to penetrate into the tube when said rst end is inserted into molten metal, said pressure reducing means comprising a cylinder defining an internal chamber having an end connected with the second lend of said tube, -a plunger reciprocably received insaid chamber an-d movable toward and away from said second end to evacuate air from said tube when moving away from said second end, and

regulatable reciprocating means comprising an electric motor operatively connected with said cylinder for reciprocating said plunger, said motor comprising a rotor and said pressure reducing means further comprising means operatively connected with said rotor and with said plunger for transforming rotary movements of said rotor into linear movements of said plunger; and adjusting means for regulating said reciprocating means and for thereby regulating the evacuating action of said pressure reducing meansV so as to insure gradual penetration of molten metal into said tube.

4. An apparatus as set forth in claim 3, further comprising means for reversing the direction of said rotor whereby the plunger is reciprocated toward and away from the second end of said tube in response to rotation of said rotor in opposite directions.

5. An apparatus for withdrawing samples from molten metal, comprising a sampling tube of heat-resistant material, said tube having a first end adapted to be inserted into molten metal and a second end; pressure reducing means connected with said second end for evacuating air from said tube and for thereby causing molten metal to penetrate into the tube when said rst end is inserted into molten metal, said pressure reducing means comprising a cylinder defining an internal chamber having .an end connected with the second end of said tube, a plunger reciprocably received in said chamber and movable Atoward `and away from said second end to evacuate air from said tube when moving away from said second end, and regulatable reciprocating means operatively connected with said cylinder for reciprocating said plunger, said reciprocating means comprising reversible electric motor means having a rotatable shaft turnable in either direction, means for preventing rotation of said plunger relative to said cylinder, threaded engagement means operatively connecting said plunger with said shaft for converting rotation of the latter in one 4direction into an axial movement of said plunger in one direction and for converting rotation of said shaft in opposite direction into axial movement of said plunger in opposite direction, reversing switch means connected with said electric motor means and movable between positions respectively determining -alternatively one of the directions of rotation of said shaft, and mechanical control means interposed between said reversing switch means and said plunger for moving said reversing switch means between its two positions whenever said plunger has completed a predetermined length of stroke in any of said directions of movement thereof so as to produce an automatic reciprocating movement of said plunger; and adjusting means for regulating said reciprocating means and for thereby regulating the evacuating -action of said pressure reducing means so as to insure gradual penetration of molten metal into said tube.

References Cited by the Examiner UNITED STATES PATENTS 1,442,444 `l/1923 Reeve.

2,083,522 `6/1937 Morgan 137-544 X 2,329,035 9/ 1943 Cross 73-49.4

FOREIGN PATENTS 743,922 1/ 1956 Great Britain.

OTHER REFERENCES General Electric News Bulletin, New York, July 12, 1948, 2 pages (copy in 73-15).

RICHARD C. QUEISSER, Primary Examiner.

JOSEPH P. STRIZAK, Examiner.

J. W. MYRACLE, Assistant Examiner. 

1. A METHOD OF WITHDRAWING A SAMPLE FROM MOLTEN METAL INTO A SAMPLING TUBE, COMPRISING THE STEPS OF MAINTAINING THE MATERIAL OF THE TUBE AT A TEMPERATURE NOT SUBSTANTIALLY EXCEEDING ROOM TEMPERATURE; INSERTING ONE END OF THE TUBE INTO THE METAL; AND GRADUALLY REDUCING THE PRESSURE PREVAILING IN THE INTERIOR OF THE TUBE BY EVACUATING AIR THROUGH THE OTHER END THEREOF IN SUCH A WAY THAT THE DROP OF PRESSURE GROWS IN DIRECT PROPORTION WITH THE TIME ELAPSED SINCE THE BEGINNING OF WITHDAWAL WHEREBY THE METAL PENETRATES GRADUALLY INTO THE TUBE. 